A two-stage evaporative cooler is a newer, more efficient evaporative cooler that uses a pre-cooler, improved evaporative pads, and a more efficient motor. The pre-cooler cools the incoming air, with a water-cooled heat exchanger, and without adding any moisture to the air. Then the air flows through the wet pads, which cool by evaporation. The pre-cooling provides an extra 3° to 9°F (1.7°C to 5.0°C) temperature drop, so the air feels drier and more comfortable compared to standard evap coolers. These relatively new coolers have increased their sales, especially in the American Southwest, as customers suffer climate-change’s extreme temperatures. Their advantages include these.

  • They reduce temperatures by 20-30°F (11-17° C) compared to ambient air.
  • Two-stage evaporative coolers aren’t rated with a Seasonal Energy-Efficiency Ratio (SEER) like air conditioners, but if they were, the SEER would be more than 40.
  • They maintain a more comfortable temperature/humidity balance, improving overall comfort in dry climates.
  • The two-stage process reduces the amount of water required for sufficient cooling.
  • Options include a filter to remove dust and pollen, improving the air quality.

A guide to low-cost cooling

Information from John Krigger’s new book: Cool Buildings for Hot Weather on sale from Saturn Resource Management or Amazon

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